1. Field of the Invention
The present invention relates to magnetic storage media from and to which information is read and written and magnetic recording and playback devices for reading and writing information. More particularly, the present invention relates to a magnetic storage medium from and to which information is read and written by using a magneto-resistive head and also to a magnetic recording and playback device, having the magneto-resistive head, for reading and writing information.
2. Description of the Related Art
As the volume of information to be processed in a magnetic recording and playback device, which records and reads data by using a magnetic tape, has been increasing recently, the magnetic tape is required to have a larger storage density. Accordingly, a magneto-resistive head (hereinafter, referred to as an MR head) is essential as a magnetic head for reading signals instead of a conventional inductive head. Because the MR head is one type of magnetic head for reading signals stored in a magnetic storage medium by using a magneto-resistive effect (hereinafter, referred to as an MR effect) of a magneto-resistive element (hereinafter, referred to as an MR element), the MR head is highly capable of detecting signals for providing large reading outputs, thereby allowing the magnetic tape to easily have a reduced recording track-width and an increased recording density in a line direction. This allows the magnetic recording and playback device to perform recording and reading data densely.
Also, a known recording and playback device using a magnetic tape is based on a helical-scan principal arranged such that the magnetic tape for recording and reading signals is wound in a helical manner around a head drum, which is rotatable together with the magnetic head mounted on the rim thereof. In the helical scan-type recording and playback device, the magnetic head records and reads signals while sliding on the running magnetic tape at a high speed, that is, the magnetic tape and the magnetic head have a high relative sliding speed, thereby realizing an improved data transfer rate.
In general, however, the MR head is more sensitive to static electricity and heat than the inductive head. FIGS. 1A and 1B show measured values of an electrostatic-discharge breakdown voltage (hereinafter, referred to as an ESD breakdown voltage) of an anisotropic magneto-resistive head (hereinafter, referred to as an AMR head) and a giant magneto-resistive head (hereinafter, referred to as a GMR head), respectively.
To obtain the values of EDS breakdown voltage, a human body model is used in which the voltage and the resistance across the MR heads, i.e., the AMR head and the GMR head, are measured as shown in FIGS. 1A and 1B for every time when charges stored in a capacitor having a capacitance of 100 pF are discharged while the capacitor is connected to a resistor having a resistance of 1.5 kxcexa9. The graphs indicate that the EDS breakdown voltages of the AMR head and the GMR are about 230 to 240 V and about 30 to 40 V, respectively. In the meantime, as will be described next, friction, contact, induction, or the like causes a charged insulator, such as plastic including nylon and vinyl in a normal condition, to easily have a voltage of higher than several kV, which far exceeds the EDS breakdown voltages of the MR heads.
Many known cassette cases for winding and housing a magnetic tape are formed of high-resistance synthetic resin materials. These cassette cases are likely charged with static electricity due to friction with, e.g., a packing material, a glove made of synthetic fiber when handled by users a component of the magnetic recording and playback device when loaded in the device. The electrification voltage of a charged synthetic material, such as ABS resin having a surface-resistance of about 1xc3x971016 xcexa9/inch2 used for the cassette cases, is 1500 to 2000 V or higher, and the half-life of the voltage is at least three minutes. Since the electrification voltage exceeds far beyond the withstand voltage of the MR head and, further, the half life is long, the electrostatic charges once generated take a long period of time to decay. Therefore, when the charged cassette case is loaded in the magnetic recording and playback device and the magnetic tape therein contacts the MR head, a large amount of current flows into the MR head through the magnetic tape, possibly causing the ESD breakdown of the MR head.
FIG. 2 is a conceptual illustration of a charge flow when the magnetic tape contacts the MR head. A head drum 80 mounted in the magnetic recording and playback device comprises a rotating drum 82 having the magnetic head, e.g., on the rim thereof, and a fixed drum (not shown). A magnetic tape 92 travels around the head drum 80 in a helical manner, and the rotating drum 82 rotates. This rotation allows the magnetic head to scan the magnetic tape 92 so as to record and read signals. FIG. 2 illustrates a part of the head drum 80 in an enlarged scale, and an MR head 81 mounted on the rotating drum 82 as a magnetic head for recording and reading signals detects stored signals in contact with the traveling magnetic tape 92.
When the cassette case for winding and housing the magnetic tape 92 is charged with static electricity, electric charges 83 start to flow from the surface of the magnetic tape 92 to the ground of the head drum 80 through the contacted MR head 81. For example, at the time of starting the reading operation of the magnetic recording and playback device, the cassette case is loaded in the device, and then the magnetic tape 92 comes close to the rotating drum 82 in accordance with the movement of a guide mechanism of the device. At the instant of the magnetic tape 92 contacting the MR head 81, a large amount of electric current flows to an MR element, causing the ESD breakdown of the MR element, and thereby resulting in the failure of reading signals in the magnetic tape 92. With this, the MR head 81 has not been available as a magnetic head of the recording and playback device using the magnetic tape 92.
The present invention is made in view of the above problems. Accordingly, it is an object of the present invention to provide a magnetic storage medium and a magnetic recording and playback device which prevent the ESD breakdown to an MR head.
To this end, in accordance with one aspect of the present invention, there is provided a magnetic storage medium from and to which information is read and written by an MR head. The magnetic storage medium comprises a magnetic tape and a pair of reels for winding and rewinding the magnetic tape, wherein the reels are provided with an antistatic treatment.
The antistatic treatment performed on the reels suppresses the generation of static electricity to the reels, thereby preventing the ESD breakdown of the MR head. Further, the reels of the magnetic storage medium according to the present invention preferably may comprise a conductive material as the antistatic treatment.
Further, the reels of the magnetic storage medium according to the present invention are preferably connected to the ground when the magnetic storage medium is loaded in a magnetic recording and playback device. Further, the surface-resistance of the conductive material for the reels of the magnetic storage medium according to the present invention preferably ranges from 0 xcexa9/inch2 to 1xc3x971012 xcexa9/inch2.
In accordance with another aspect of the present invention, there is provided a magnetic recording and playback device. The device comprises an MR head and a pair of reel supports for supporting a pair of reels of a magnetic storage medium loaded in the device, wherein the reel supports are provided with an antistatic treatment.
The antistatic treatment performed on the reel supports for supporting the reels of the magnetic storage medium loaded in the device suppresses the generation of static electricity to the reel supports and, thereby, prevents the ESD breakdown of the MR head. Further, at least one part of the reel supports of the magnetic recording and playback device according to the present invention may comprise a conductive material as the antistatic treatment.
Further, at least one part of the reel supports of the magnetic recording and playback device according to the present invention is preferably connected to the ground. Further, the surface-resistance of the conductive material for at least one part of the reel supports of the magnetic recording and playback device according to the present invention preferably ranges from 0 xcexa9/inch2 to 1xc3x971012 xcexa9/inch2.
Further, in accordance with still another aspect of the present invention, there is provided a head drum for reading and writing information from and to a magnetic tap. The head drum comprises a conductive rotating drum at the ground potential, around which the magnetic tape is wound in a helical manner, a metal base fixed inside the rotating drum and electrically connected to the rotating drum, and a magnetic head fixed to the metal base. The magnetic head comprises the following components: a head substrate and a protection substrate, both having a resistance of 1xc3x971010xcexa9 or less and electrically connected to the metal base; a pair of outer insulating films disposed between the head substrate and the protection substrate; a pair of magnetic shielding films disposed between the pair of outer insulating films; a pair of inner insulating films disposed between the pair of magnetic shielding films; and an MR head element for reading stored signals by contacting the magnetic tape disposed between the pair of inner insulating films.
The head substrate and the protection substrate of the head drum may comprise a conductive material having a resistance of 1xc3x971010 xcexa9 or less and may be electrically connected to the metal base so as to be at the ground potential via the metal base and the rotating drum. This treatment allows static electricity charged on the magnetic tape to be discharged to the head substrate and the protection substrate without flowing to the MR element, thereby preventing the ESD breakdown of the MR element.
As described above, the reels of the magnetic storage medium of the present invention are provided with an antistatic treatment, thereby suppressing the generation of static electricity during loading or operating the magnetic storage medium and preventing the ESD breakdown of the MR head.
Further, the reel supports of the magnetic recording and playback device of the present invention are provided with an antistatic treatment, thereby suppressing the generation of static electricity during loading or operating the magnetic storage medium and preventing the ESD breakdown of the MR head.
Still further, the head substrate and the protection substrate of the head drum of the magnetic recording and playback device according to the present invention comprise a conductive material having a resistance of 1xc3x971010xcexa9 or less, and they are electrically connected to the metal base so as to be at the ground potential via the metal base and the rotating drum. This treatment allows static electricity charged on the magnetic tape to be discharged to the head substrate and the protection substrate without flowing to the MR head, thereby preventing the ESD breakdown of the MR head.